package auto.test;

//抽象父类
public abstract class Father {
    public Father() {
        // TODO Auto-generated constructor stub
        oupPut();  //实例化时调用，子类有，就调用子类方法，子类没有，就调用父类方法
    }
    //父类抽象方法，让子类重写
    public  void  oupPut(){
        System.out.println("from Father class");
    };
}
//子类A
class ChildA  extends Father{
    //重写父类方法
    @Override
    public  void  oupPut(){
        System.out.println("from childA class");
    }
}
// 子类B
class ChildB extends Father {
    //重写父类方法
    @Override
    public  void  oupPut(){
        System.out.println("from childB class");
    }
}
class ChildC extends Father {
    //没有重写父类方法

}

执行测试类
public class TestClaass {

    public TestClaass() {
        // TODO Auto-generated constructor stub
    }
    public static void main(String arg[]){
        Father a = new ChildA();
        Father b = new ChildB();
        Father c = new ChildC();
    }
}